Method of press-molding thermoplastic resins

• Main Authors: KITAYAMA; TAKEO, TOGAWA; YOSHIAKI, NAKAMURA; YUKITO, TSUTSUBUCHI; MASAAKI, MATSUMOTO; MASAHITO
• Format: Patent
• Language: English
• Published: 18.08.1998
• Edition: 6
• Subjects: AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING; INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS; PERFORMING OPERATIONS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDEDFOR; SHAPING OR JOINING OF PLASTICS; TRANSPORTING; WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE, IN GENERAL

A thermoplastic resin is molded by a press-molding method wherein a thermoplastic resin in a molten state is compressed to flow between a pair of female and male molds so as to be formed into a predetermined shape. A compression rate of the mold is controlled so that the following expression (1) is satisfied: 0.5 APPROXLESS B/A APPROXLESS 2(1) wherein A (mm/s2) is an acceleration which is realized at a time when the compression rate is 75% of a maximum rate in a compression-acceleration region, which region is defined as a period of time from a moment when the compression of the molten thermoplastic resin is started to a moment when the compression rate reaches the maximum rate; and B (mm/s2) is a deceleration which is realized at a time when the compression rate is 75% of the maximum rate in a compression-deceleration region, which region is defined as a period of time from a moment when the compression rate reaches the maximum rate to a moment when the closing of the molds is complete. By this method, a molded article having excellent surface appearance free from unevenness of gloss and surface irregularity can be obtained.